Desalination process



DESALINATION PROCESS 2 Sheets-Sheet l Filed DGO. 26, 1967 QN .\Ox UU wi1 n m MMCOQUXW M A k L 49; QB MWB E Oct. 15, 1968 R. E. ANDERSONDESALINATION PROCESS 2 Sheets-5heet 2 Filed Dec. 26, 1967 1N VENTOR.

/07' TOR/VE VS oe/WLE Hr) ole/"son nited States Pater 3,406,113DESALINATION PROCESS Robert E. Anderson, Midland, Mich., assignor to TheDow Chemical Company, Midland, Mich., a corporation of Delaware FiledDec. 26, 1967, Ser. No. 693,325 12 Claims. (Cl. 210-30) ABSTRACT vor*.THE` DIsCLosURE' An ion exchange process isV provided for thedesalination of'wate'r. The process includes regeneration of the cationexchange resin with a complex sulfonic acid and regenerationV of theanion exchange resin with sodium sulte. Preferably, the regenerantefuents of both ion exchange resins are mixed and this mixture isdistilled to substantially recover thecomplex sulfonic acid and sodiumsulteregenerants for reuse.

Background This invention relates to a process for the desalination ofwater. More particularly, it relates to the desalination of water by anion exchange process which includes regeneration of the ion exchangematerials, and recovery and recycle of the regenerants used intheregeneration process.

' Many methods have been proposed in the past fordemineralizingwater,including thermal distillation, freezing, dialysis,ion exchange techniques, and the like.

.-In conventional demineralization processes utilizing ion exchangetechniques, a cation exchange-resin is used to remove metal cations,primarily sodium, magnesium, and calcium, from the water; and an anionexchange resin is used to remove anions, primarily sulfate, chloride,and carbonate from Vthe water. The result of this dual resin treatmentis the essentiall replacement of the cations in the water with hydrogenions provided by the cation exchange resin. These added hydrogen ionsconvertthe anions in the water into-acids and the removal of these acidsiS then achieved with an anion exchange resin.

Conventional ion exchange systems are largely discontinuous and the highchemical costs of regeneratingthe resins, together with the problem ofdisposing of voluminous amounts'of wastes produced in such regeneration,have made ion exchange processes uneconomical, except in thedemineralization of water with a relatively low solids content. Thus,such processes have not heretofore been used'ini-desalination where thewater being treated often contains 102-104 times the amount of dissolvedsolids that can be economically treated in conventional ion exchangedemineralization processes.

It is therefore a primary object of this invention to provide a new andimproved process for the desalination of water that can effectivelyremove the large amounts of dissolved salt from the water toeconomically produce a potable water product.

Another object of this invention is to provide an ion exchange processfor the desalination of water in which the elluent from regeneration ofthe cation exchange resin can be used to regenerate the anion exchangeresin.

Still another object of this invention is to providean ion exchangeprocess for the desalination of water using a cation exchange resin andan anion exchange resin in which the regenerant for the cation exchangeresin ils'recovered from the cation regenerant efuent, and the remainderof the cation eiuent is used to regenerate the anion exchange resin.

Yetanother object of this invention is to'l provide an ion exchangeprocess for the desalinationof .water in which .the Aregenerants forthe'cation and anion exchange materials are recovered and usedltominimize regenerant waste and substantially reduce the cost ofreplenishing regenerant chemicals. Y l

A further object of this invention is to;provide anion exchange,desalination process in which a complex sulfonic acid is used as theregenerant for the cation eX- change material. y

Yet a further object of this invention is to provide an ion exchange,desalination process in which a complex sulfonic acid is used as theregenerant for the cation exchange material and in which sodium sulte,produced in the regeneration of the cation exchange material is used asthe regenerant for the anion exchange material.

Still a further object of this invention is to provide a continuousprocess for the desalination of water that can be carried out in asimple, elective, and economical manner.

Additional objects and advantages will be set forth in part in thedescription which follows, and in part will be obvious from thedescription or may be learned by p'ractice of the invention, the objectsand advantages being realized and attained by means of the methods,improvements, and combinations of steps particularly pointed out in theappended claims.

Statement ofjhe invention To achieve the foregoing objects and inaccordance with its purpose, this invention, as embodied and broadlydescribed, provides a process for the desalination of water containingdissolved, inorganic salts of (a) bivalent cations, (b) monovalentcations, including sodium, and (c) anions, which comprises: (A) bringingthe salt-containing water into contact with a cation exchange resin inhydrogen form to remove the cations of the salts and-produce a firsteiiiuent containing acids of the anions; (B) regenerating the cationexchange resin by contacting it with a complex sulfonic acid comprisingthe reaction product of sulfur dioxide, water, and a water-solublealdehyde or ketone thereby removing the cations from the resin restoringthe resin to hydrogen form, and producing a second effluent containingorganic sulfonates of the cations; (C) contacting the r'stacid-containing efliuent from the cation exchange resin with a weak baseanion exchange resin to remove the acid anions and produce an effluentfrom the anion removal material which comprises substantiallydesalinized water; (D) heating the second eflluent from the cationexchange resin, containing the organic sulfonates, to recover thealdehyde or ketone, a portion of the sulfur dioxide, and a solutioncontaining sodium sulte; (E) recycling the recovered aldehyde or ketoneand sulfur dioxide to at least partially regenerate the cation exchangeresin, and (F) contacting and at least partially regenerating the anionexchange resin with the sodium sulte solution.

In accordance with a preferred embodiment of this invention in which thebivalent cations in the water include calcium and the anions includesulfate, the second effluent from the cation exchange resin is mixedwith an effluent produced byregeneration of; the anonexchange resinlwithsodiumsulte. .This mixing ofthe eifiuents produces insoluble calciumsulfate, uwhich .can, be- ,easi1y removed .from the mixture, and theAcombined 'efuents are then heated to substantially recover the aldehydeor ketone. and` sulfur .dioxide and provide'a sodium sultesolutionsuitable for regeneration of the anion. exchange resin.Furthermore a continuousow of cation exchange resin countercurrent tothe feed and regenerant streams is preferred. YAlso vwaterfsoluble C1-C8aldehydes and ketones arey particularly suitable for use in theregenerant solution.

Description The accompanying drawings, which are incorporatedY inand"constitute a part of this specification, illustrate the presentlypreferred embodiments of theinvention and, together with thedescription, serve to'explain the principles of this invention."

Of'thedrawings:

'FIG. 'I is ai s'chematic'diagram ofthe ion exchange process of'thisinvention showing the recovery of the' cation' exchange resinregenerant from lthe cation regenerant' etilue'nt, the recyclingof thecation exchange regenerant to the cation exchange resin, and theregeneration of the anion exchange resin with the remainder of thecation regenerant etuent; and

FIG. 2 is a schematic diagram of an alternative embodiment of the ionexchange process of this invention showing recovery and recycling of theregenerants for both the cation exchange resin and the anion exchangeresin.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory but arenot restrictive of this invention.

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

The ion exchange systems of this invention, like other ion exchangesystems known in the art, are equilibrium systems both in the ionexchange phase of the process and in the regeneration phase. Theinvention utilizes ion exchange resins that are brought into contactwith the water-to be desalinized. These resins may be used in either theform of a lixed bed through which the water and then the regenerant arepassed; or in the form of a.' moving bed, in which the resin is broughtinto cont-act with the water in an ion exchange vessel, and thendischarged to a regeneration vessel and subsequently recycled to the ionexchange vessellndeed a countercurrent, continuous ion exchange reactorof the type described by Higgins, U.S. Patent 2,815,322 is particularlysuitable for use in the process of this invention.

While the process of this invention will be described as it relates to asingle xed bed of resin, it is to be understood that the process isequally applicable -to a moving bed method and to tandem fixed bedmethods where one bed is removing ions while the other is regenerating.

As shown in FIG. 1, the water to be treated by the process of thisinvention is initially contacted with a cation exchange material incation-exchange reactor 10. The most predominant cations in water aresodium, calcium, and magnesium ions and the most predominant anions arechloride, sulfate, and carbonate ions. Generally, it is desired toremove suicient amounts of these ions from the water to produce apotable water product containing less than 500 p.p.m. of dissolvedsalts.

Gatien-exchange reactor contains a cation exchange resin in the hydrogenform. The hydrogen ions from this resin are exchanged with the metalcations in the water in reactor 10. The cation exchange resins whichcanbe used in the process of this invention include sulfonic acid resinssuch as the sulfonatedvstyrenedivinylbenzene copolymer resinscommercially available under the trade names Dowex 50W-X8 from The DowChemical Company, "Amberlite lR-l from Rohm and Haas Co., Ionac C-24O`from fthe Ionac Chemical Co.,` vand lthelike. vA preferred cationexchange resin `foruse-inuthelprocess of this invention isDowex 50 X8resin. e v ,s -The water tobe treated ispassed throughthe cation exchange resin where `the hydrogenionsffinthe resin are exchanged forthemetal cations of "the dissolved salts in the water. The reactionswhich occ-'ufr in the cation exchange 'resin can be exemplitiedby'the'fllowing equation in which RSO3Hrepresents a sulfonicacid cationex-v changeresin: i .A l

'fhe cations of the'inorganic salts'win thefwater are thus adsorbed bythe resin and they anions converted to their respective' acids,producing an eluent Astream 12 lfrom. reactor .'10 whichcontairishydjrochloric', sulfuric, and carbonio acid'. The carbonic acidwhich is formed .may decompose totally or in part into water and carbondioxide gas. y

In accordance with this invention, effluent 12'froin cation exchangereactor 10, which contains .acids of the inorganic salts, is passedthrough an anion lexchange reactor 14 to remove these acids and producea desalinized water product.

Anion exchange reactor 14 preferably contains a weakbase anion exchangeresin that adsonbs the inorganic acid anions by forming acid salts ofthe resin. Resins 0f this type, which are waterinsoluble crosslinkedpolymers containing primary, secondary' and tertiary amino groups, arecommercially available Iunder the trade names Dowex 44 (The Dow ChemicalCompany), 'Duolite ASOB (Chemical Process Co.), and Amberlite Ill-45"(Rohm & Haas) resins. A preferred anion exchange resin for use in theprocess of this vinvention is Dowex 44 resin.

The reactionv which occurs in anion exchange reactor 14 can beexemplified by the followingequation in which RSN represents theaninexchange resin:

Hol

COni'HgO In this reaction, the chloride and sulfate anions in effluent12 from cation exchange reactor 10 are adsorbed BaN-HC1 by the anionexchange resin, producing a water product 16 from which the dissolvedinorganic Asalts have been substantially removed. Any remaining carbonioacid in thev solution can be removed by aeration.

In accordance with thisinvention, the spent or partially spent cationexchange resin containing the metal cations of the inorganic salts isregenerated by contacting it with a complex sulfonic acid solution suchas `described by Wilson,'U.S. Patent '3,248,278'. The complex sulfonicacid is prepared by adsorbing sulfur dioxide in. an aqueous solution ofa vsuitable water-soluble aldehyde or ketone to produce a strong complexsulfonic acid by the reaction:

is the aldehyde or ketone. The complex` sulfonic acid (ZSO3H)-fis afhighly etfectivercation exchange resin rregenerant in thepresentsysternrgt, l

Exemplary of.V carbonyl compounds vsuitafhle for use in the preparationof the complex sulfonic acid are watersoluble Cl-Cg aldehydes orketones, such as acetone, methyl ethyl ketone, acetaldehy'de,Afurfuraldehyde,L isobutyraldehyde, cyclohexanone, formaldehyde,`benzaldehyde, methyl isobutyl ketone, mesityl oxide, andsalicylaldehyde. Acetone is preferred for use in the process of thisinvention and reacts with sulfur dioxide and water to produce2-hydroxypropane-2-sul'fonic acid.

At room temperature maximum ionization of the complex-sulfonic acid canbe,most economically achieved at a weight ratio of water to acetone ofabout 7. to l. Increasing the proportion of acetone to water above about7 to 1 only insigniiicantly increases the solubility of sulfur dioxidein the mixture. An optimum acid composition is achieved using aminimumeffective amount of acetone, because acetone is the .most expensivereagent in the system and `because large amounts of water in thesolution produce maximum ionization of the acid. At a weight ratio ofseven, parts water to one part acetone, the complex sulfonic acidsolution contains approximately 11% acetone, 12% sulfurdioxide and77%water and has a normality roughly equivalent to a 2 N acid.

The complex sulfonie acid stream 18 containing H+ cations and Z803*anions is passed through the spent cation exchange resin in reactor toremove the metal cations from the resin. In this regeneration, thehydrogen ions of the sulfonic acid are exchanged for the metal cationsadsorbed by the cation exchange resin and this regeneration reaction canbe exemplified 'by the following equation: l

The metal cations are thus removed from the resin as organic sulfonatesand the resin is returned to the removed from the cation regeneranteluent in filter 28 are a source of additional sulfur dioxide, and canbe used to prepare the complex sulfonic Iacid regenerant. In accordancewith one embodiment of this invention, therefore, these salts arecalcined in calciner 32 by heating them, in the case of magnesiumsulfite toaround 600 C., and in the case of calcium sulfte to aroundl200 C. This calcining decomposes the sulfte salts into their respectiveoxides and sulfur dioxide. The additional quanti,- ties 0f sulfurdioxide recovered by calcining substantially reduce the amount of sulfurdioxide from an external hydrogen form for further desalination.V Themetallo- I organic sulfonates formed in the cation regeneration reactionare relatively water-soluble, and the regenerant eiuent stream 20 fromcation-exchange reactor 10 thus contains sodium, calcium, and magnesiumsulfonates.

In accordance with this invention, regenerant effluent stream 20 isvtreated to recover the carbonyl compound and a portion of the sulfurdioxide for `further use in regenerating the cation exchange resin. Thisrecovery procedure ncanine carried out fby VHash distillation at about100 C. in a suitable vessel 22 in which the carbonyl compound, a portionof the sulfur dioxide, and some waterfare stripped from the efiluent asdistillate stream 24. Since al1 of this distillate is to be laterrecombined to again form the complex sulfonic acidit is immediatelypassed to regenerant make-up yvessel 26 without sepa'- K y rating eachof its various components.`

Distillation of the cation regenerant eluent 20 is exemplified by thefollowing equation: 1

where R' is the aldehyde or ketone originally used to produce thecomplex sulfonic acid regenerant. Y

The residue 27 exiting distillation vessel 22 contains water, andsodium, calcium and magnesium sulftes. The sultes of calcium andmagnesium are linsoluble in water and precipitate out of residue 27.These insoluble :sultes are removed by` filter 2S, leaving a finalstream 30 comprising an aqueous sodium sulfte solution. y

Only about one-half of the sulfur dioxide in the sulfonic acidregenerant isrecovered by the distillation' in vessel 22, with the`remainder-forming sulfites of the metal cations in the cation regeneranteffluent. Thus, additional sulfur dioxide must usually be added tomake-up tank 26 to provide the sulfonic acid concentration necessary toachieve subsequent regeneration of the cation exchange resin.

The insoluble sulfte salts of calcium and magnesium source that must beadded to make-up tank 26, thereby further economizing the process ofthis invention.

The aqueous sodium sulfte solution 30, resulting from distillation andfiltration of cation regenerant effluent 20, is used as the regenerantfor the anion exchange resin in reactor 14. The -amount of sodium ionsin solutionv 30 necessary to regenerate the anion exchange resin, ,is dependent upon the relative amounts of sodium and alkaline earth ions inthe water treated by the process of this invention. Additionalquantities of alkaline material, such as sodium hydroxide, therefore,may need to be added to the sodium sulfte solution to make up the amountof base material needed to regenerate the resin. The use of the sodiumsulfte from treated cation efuent20, however,l reduces, at least in partand perhaps in Whole, the quantities of alkaline material that must beadded from an external source to effect regeneration of the anionexchange resin. Regeneration of the anion exchange resin can beexemplified as follows:

The presence of sodium hydroxide in the anion exchange resin regenerantreduces the amount of sodium bisulfite -produced in the regeneration byreacting with a .portion of the hydrogen ions of the acids to formwater. This reaction can be exemplified yas follows:

Anion regenerant effluent 34 is generally discarded as regenerant waste.However, additional quantities of sulfur dioxide for use in regenerationof the cation exchange resin can be recovered if desired by heating thesodium bisulfate-bisulfite mixture.

In accordance with an alternative and preferred embodi ment of thisinvention, anion regenerant eiuent 34 is more efficiently used as asource of additional sodium sulfte for regeneration of the anion removalresin, and as a source of sulfate ions to be used in the removal ofcalcium ions from cation regenerant effluent 20.

In this preferred embodiment of the invention illustrated in FIG. 2,anion regenerant effluent 34 is mixed with cation regenerant eiiiuent 20in mixer tank 36 prior to distillation of the combined effluents torecover sulfur dioxide and the carbonyl compound. By mixing the tworegenerant effluents, insoluble calcium sulfate is precipitated.

After removing the calcium sulfate from the combined efuents in filter38, the efuent mixture is flash distilled in vessel 22 to recover thecarbonyl compound and a major portion of the sulfur dioxide asdistillate 24. Distillation of the combined effluents leaves a liquidresidue containing magnesium sulfte, sodium sulfte, and the inert saltssodium sulfate and sodium chloride. f

Insoluble magnesium sulfte is formed during the distllation by thedecomposition of magnesium sulfonate.

This magnesium sulfte is removed from the effluent in filter 28, andcalcined in calciner 32 to recover additional quantities of sulfurdioxide for use in cation regenerant solution 18. The removal ofmagnesium sulte leaves a nal stream 30 comprising substantially anaqueous solution of the sodium suliite originally used to regenerate theanion removal resin, along with inert sodium lsulfate and sodiumchloride. l

Solution 30 is then recycled -to reactor 14 Aas thefregenerant for theanion exchange resin, with additional quantities of sodium hydroxidebeing Vadded atV 31, if needed, to provide the required sodium ionconcentration'. While the inert sodium saltsdo not adversely eiect re"-generation of the anion exchangefresin, they preferably should becontinuously bled from the system to prevent them from building up andmechanically affecting the operation of the process of this invention. f

By combining 'anion and cation regenerant eiu'ents 20 and 34 in themannerdescribed above, rather than merely disposing of the anionregenerant etiluent, substantially increased quantities of sulfurdioxide can be recovered during distillation because the 'sulfurdioxideis no longer needed to form the sulte salts of calcium. Thisrepre sents a more economical procedure 'for the recovery of sulfurdioxide because calcium sulte must be'heated to about 1200 C. to recoverits sulfur dioxide content, whereas distillation recovery of sulfurdioxide in accordance with the preferred form of this invention can= beaccomplished at temperatures of about 100'l C. or less. The preferredembodiment of this invention, therefore, provides a more `economicalprocess for the recovery of sulfur dioxide. Further, by calcining themagnesium sultite above, as shown in FIG. 2, substantially all of theoriginal sulfur dioxide content in the regenerant can be recovered.

By combining the regenerant efiiuents, it is also possible toeconomically recover sodium sultite from the anion regenerant effluentfor reuse in the regeneration of the anion exchange resin. Duringregeneration of the anion exchange resin with sodium sulti-te, sodiumbisulte is formed due to the presence of the hydrogen ions in the acidsadsorbed by the resins. By mixing the eiuents in mixer tank 36, thisbisulte compound is converted back to sodium sulte, generally in anamount equivalent to that initially used to regenerate the anionexchange resin.

While aditional quantities of alkaline material may need to be added tothe solution in some cases to provide required concentrations of sodiumions, once the process has been initiated with the required amounts ofsodium sulfite, the need for addition of sodium hydroxide at 31 will beminimized if not eliminated altogether.

The reactions believed to occur between the mixed regenerant effluentsin tank 36 can be summarized as follows:

.Anton Regenerant Cation Rcgenernnt NaHSO; -i- 2NaHSO4 Ca(ZSO3)2 NaZ S0@Mixed Etluents Casoni, -i- NB2SO4 -i- NazSOg -I- SZSOgH The calciumsulfate is removed by filter 38, the sulfonic acid is removed indistillation tank 22, and sodium sulte solution 30, containing inertsodium sulfate, is recycled to reactor 14 as the regenerant for theanion exchange resin.

It will therefore be apparent from the foregoing description that thisinvention provides simple, economical, and effective methods for thedesalination of water having several important advantages not heretoforerealized in prior art processes. Such advantages include substantialelimination of the problem of disposing of waste materials, byconverting por-tions of the salts in the water into usable or easilydisposable byproducts, and by utilizing other portions as regenerantsfor the ion removal resins.

Further, the chemical agents used in the process to regenerate theresins are substantially recovered, thus allowing the process to operateeconomically and continuously in the desalination of water containing ahigh degree of dissolved solids.

For a clearer understanding of this invention, specific examplesofit-are set forth below. These examples are merely illustrative 'and arenot intendedto limit the scope and underlying principles of thisinvention in any way. s

:` EXAMPLE 1 Regenerqnt solution :A

.This example illustrates the preparation ufl-hydroxy'-propane-Z-sul-foniciacid as a regenerant for the cation exchangeresin.-.1. Y

`The complex-sulfonicacid is prepared by adsorbing sul-fur dioxide gas`in various mixtures of water and acetone in'a gas adsorption column.The yadsorption column consists ofla l-inch glass tube lled to a depthof 8 inches with berlsaddles.' The column is topped with a 3bulbcondenser.

Sulfur dioxide is fed into the bottom of the column through afritted-glass sparger located just below the packingk'The liquidYmixture of acetone and water is then introduced above the packing bymeans of a pump. The liquid -mixture drains down through the packing andout the bottom of the column into a 2liter 'flask fitted with a reuxcondenser. Condensate from the reflux condenser is vrecycled backthrough the pump and into the top of the gas adsorption column.

The adsorption column is operated for various periods of time todetermine the optimum ratio of acetone to water at maximumconcentrations of sulfur dioxide. The results of several runs made atroom temperature are set forthl below in Table I.

TABLE I Weight ratio of Contact time Normality of acid H2O/acetone(hrs.)

1 l 1.8 lower phase 1% l2.09; p=1. 072 13.43; p=0. 989 2 1. 95 3 2 2. 481 1. 7 4 2. 1 2 0. 42 3 1. 0 5 1. 96 1 0. 87 2 1. 45 3 1. 64 4 1.72 5 1.90

EXAMPLE 2 Desalz'naton of bracksh water This example illustrates thedesalination of water according rto the preferred embodiment of thisinvention and the recoveryand recycling of the regenerants to the cationexchange resin and the anion exchange resin.

VBrackish water containing the following concentration of metal cationsand `anions,.in milliequivalents per liter (meq./l.), is used in thisexample.

Cations Anions Ca++ 9. 50 Cl 0. 30 Mg* 6. 25 S04' 15. 90 Na+ 4. 25 CO33. 80 4'20.00 20.00.

Catz'on exchange The brackishl water containing 2() meq./l. ofthecations recited above is passed through a cation exchange reactorcontaining Dowex 50W-X8 resin having an operating capacity of `1.4meq./ml. The reactor, therefore, requires at least 14.3 ml. of resin (20meq./l./1.4 meq./ml.) to remove the Vcations in each liter of waterpassed through it.

The metal cations in the iniluent brackish water are Asubstantiallyadsorbed by the resin in the cation exchange reactor, by exchange withH+'ions in the resin to produce the corresponding acids of the anions inthe water. The etiluent from the reactor has the following ionconcentrations in meq./l.

Cations Anions H+ 16.2 soi- 15.9 l oi- 0.3

The effluent ,also contains 1.9 mmoles of carbon dioxide and H2O, thedecomposition products of the carbonic acid'formed in the cationexchange reactor.

Anon exchange ""Thaii'iion exchange reactor produces a first effluent Whaving been adsorbed by t-he resin.

Rlegeneration of cation exchange resin The spent cation exchange resinis regenerated with the 2 N (2 meq./ml.) Z-hydroxypropane-Z-sulf0nicacid prepared in Example 1. Since the resin contains 20 meq./l. ofcations, 10 ml. (2O meq./l./2 meq./ml.) of the sulfonic acid is requiredto remove the cations in every liter of water which has been passedthrough the resin. A total of 14.3 ml. of the sulfonic acid (28.6 meq.)per liter of water previously treated are used to insure regeneration ofthe resin to a suitable operational level.

The regenerant etiluent contains the following concentrations of ions inmeq. per liter of water treated, 20 meq. of H1L ions (per liter of waterinitially passed through the resin) having been adsorbed by the resinand exchanged for the cations. Z represents the radical 2-:hydroxypropane in the sulfonic acid anion.

Cations Cat-t 9.50 Mg++ 6.25 Nar 6.25 H+ 8,60

Regeneration of the anion exchange resin Cations Anions Na+ v 18.3 Cl-0.3 H803- 7.9

HSOr 5.9

Recovery of regenerants from` regenerant )effluents Cations Anions Ca++9.50 Cl- 0.3 Mg++ 6.25 HSOa- 7.9 Na+ 22. 55 HSOF 8. 0 H+ 8.60 ZSOS- 28.6

Mixing the effluent from the cation exchange resin, containing metalsulfonates, with the efiluent from the anion removal resin, containingbisulfates and bisulfites precipitates about 0.646 (9.5 Inmole)/l. ofcalcium sulfate. After removing Vthe'CaSO.; byiltration, the remainingsolution is ash distilled to recover substantially all the acetone, 25.4-mmoles of sulfur dioxide, yand some, H2O. Removal of SO2 from themixture during distillation produces a precipitant of .325 gm./l. ofmagnesium Sullite (6.25 meq. of Mg++ and 6.25 meq. of SO3=).

After filtering olf the magnesium suliite, the supernatant portion ofthe distillation residue, consisting pre-` dominantly of sodium suliteand small amounts of inert sodiuml chloride and sodium sulfate has thefollowing ion concentrations in meq. per liter of water treated.

Catlons Recycling of cation regenerant The distillate from the mixedeluents, containing acetone, sulfur dioxide, and water, is recycled as aregenerant to the cation exchange resin. The distillate contains 25.4mmoles of SO2 (per liter of water treated) that is capable of providing25.4 meq. of sulfonic acid. Since 2.8.6 meq. of the sulfonic acid isrequired to insure regeneration of the cation exchange resin, 3.2mmoles/l, of SO2 are added to fortify the cation regenerant and providea sulfonic acid solution having the necessary ion concentration.

Recycling of anion regenerant The supernatant portion of thedistillation residue, containing sodium sulte, is recycled as theregenerant for the anion exchange resin. The supernatant contains 15.75meq. (per liter of water treated) of sodium sulte. Since 18.3 meq. ofsodiuun ions are required to insure substantial regeneration of theanion exchange resin, 2.55 meq.

(iper liter of water treated) of sodium hydroxide arel f added tofortify this regenerant. The regenerant thus contains 18.3 meq. of Na+,15.75 lmeq. of SO3=, and 2.55 meq. of OH-, plus the inert sodiumchloride and sodium sulfate salts as shown above.

EXAMPLE 3 Sulfur dioxide recovery The magnesium sullite precipitateresulting from distillation of the regenerant eflluent mixture inExample 2 is calcined at 600 C. to produce magnesium oxide and 3.12mmoles of sulfur dioxide per liter of water treated.

The sulfur dioxide is then recycled to the cation regenerant. Thisadditional source of SO2, in combination withY the SO2 in thedistillate, as shown in Example 2, substantially eliminates the need foradding SO2 to the regenerant from an external source.

Cations 'i`lie regenerant effluenti is flash distilled VVto recoversubstantially acetone, 18.6 mmoles of sulfur dioxide and somewater.Removal of sulfur dioxide from the efuent during distillation produces aprecipitate of .325 gm./l. of magnesium sultite (6.25 meq. of Mg++ andl6.25 meq.

sabana generant. This .additional `sourcegoi, sulfucpdioxide, incombination with `theSO2 .inthe distillate in l'xarnple4, substantially,reduces, the.A amount ,of SO2J required .to be added-,to the regenerantrfroxnan .externalsourca EXAMPLE, 6

To further demonstrate the advantages'f 'obtainedxby mixing the eluentsfiornthe anin'exchange n V'fcatibn exchange resins, a samplecoispondiiigto`the tion of a typical'cation :regenerant eftiuent'Y`ispreparet1' from magnesium,.calcium, and 4sodiurri`hydxidesyfoiivoxides), and the su'lfonic'acid produced `in`Exarnpl'e'A1..

The concentrations' oftne metal 'cations andktfone" acid anions,`as'rneasr'ed :inumrnoles f S0322 in Table II below. h K A typical 'anionregenerant effluent Lc`c i r1p;o`s1 ion kisfalso prepared by.diSS'l'i/iil's.cslsfd ainmit O'f.' NfzSOt, NjaHsogNeHsoi, aria'Naol'jin wager; The concentrations of sodium ions and of these' anionsvarealsfo shown in Table II below. p l'. 'pflfhe prepared regeneranteiuents are lthenv ltered ytofremove Aany precipitatels`y,"`anddistilled. The

ofSO3=) and .570 gen/l. of calcium sultte (9.50 meq. 25 precipitates,distillate, and residue following distillation of Cat+ and 9.50 meq. of803:).

are analyzed.

TABLE II Ions (meq.) Regenerant etiluent Na+ Ca++ Mgt-t H+ SO; Cll S02Volume (mutans) "(mr.)-

I Catton 85 Anlon:

NaEISO3 183 159 6 140 After filtering ot the magnesium and calciumsulites, the supernatant portion of the distillation residue consistspredominantly of sodium suliiite (4.25 meq. of Na+ and 4.25 meq. ofSO3=).

Recycling of cation rcgenerant The distillate containing acetone, sulfurdioxide, and water, is recycled as a regenerant vto the cation exchangeresin as shown in Example 2. The distillate contains 18.6 mmoles of SO2(per liter of water treated) that is capable of forming 18.6 meq. ofsulfonic acid. Since 28.6 meq. per liter of water treated of thesulfonic acid is required to insure regeneration of the cation exchangeresin, 10.0 mmoles/l. of SO2 are added to fortify the cation regenerantand provide a sulfonic acid solution having the necessary ionconcentration.

Regeneration of the anion exchange resin Sulfur dioxide recovery Themixture of magnesium sulfite and calcium suliite, resulting fromdistillation of the cation regenerant effluent in Example 4, is calcinedat rst 600 C. and then at 1200 C., to produce magnesium oxide, calciumoxide, and 7.8 mmoles of sulfur dioxide per liter of water treated.

The sulfur dioxide is then recycled to the cation re- The results ofthis example show that approximately of the calcium ions in the cationregenerant effluent precipitate out as CaSO4-2H2O. Further, 'the amountof SO2 left in the solids after distillation corre, sponds roughly tothe sultes of the Mg++ and remaining Ca++`ionsin the residue.

-This invention in `its -broader aspects is not limited tothe specificdetails 'shown and described and departures may be madey from suchdetails within the spirit and scope of the accompanying claims withoutdeparting from the principles of the invention and without sacrificingits chief advantages.

1. A process for the desalination of watercontaining dissolved inorganicsalts of monovalent cations, including sodium; biva-lentl cations; andanions; which com- (A) bringing the water'into contact with a cationexchange resin in hydrogen fornito remove the cations of the salts andproduce a rst efuent from the cation exchange resin containing acids 'ofthe yanions of the salts;

(B) regenerating the cation exchange resin -by contacting it with acomplex sulfonic acid solution comprising thereaction product of sulfurdioxide, water;

V'anda water-soluble aldehydeor ketone to remove the cations from thecation exchange resin, restore it f to the hydrogen form,v andprodu'ceaa" second leitiuent containing organic sulfonatesof thecations;

(C) contacting the iirsbacididontainin'gf eliientfivith avweakly basicanion `exchang"e"resinv to remove the lacids lin the -eluentandprodu'cefan euentf from the anion exchangev resincontaningsubstantially de- -salinized W'a'ter" (D) heating the secondeffluent" from the c tion exchange material L5to-breakdowrltth'e'forg'anic is'l'fonatesia'ld s'ub'staritiallyE removetheldehydoiiketone and a portion of the sulfur dioxide from the 13eiuent, and produce a solution containing sodium sulte;

(E) recycling the recovered aldehyde or ketone and sulfur dioxide to atleast partially regenerate the cation exchange material; and

(F) contacting and at least partially regenerating the anion exchangeresin with the sodium suliite solution.

2. The process of claim 1 using a water-soluble Cl-Cs aldehyde orketone.

3. The process of claim 1, in which insoluble sultes of the bivalentcations are also formed during heating of the second efliuent from thecation exchange material, and in which lat least one of these sultes iscalcined to recover sulfur dioxide for reuse in the cation exchangeregenerant solution.

4. The process of claim 3, in which the bivalent cations include calciumand magnesium.

5. A process for the desalination of water containing dissolvedinorganic salts of monovalent cations, including sodium; bivalentcations, including calcium; and anions, including sulfate; whichcomprises:

(A) bringing the Water into contact with a cation exchange resin inhydrogen form to remove the cations of the salts and produce a rsteffluent from the cation exchange resin containing acids of the anionsof the salts;

(B) regenerating the cation exchange resin by contacting it with acomplex sulfonic acid solution comprising the reaction product of sulfurdioxide, water, and a water-soluble aldehyde or ketone to remove thecations from the cation exchange resin, restore it to the hydrogen form,and produce a second effluent from the cation exchange materialcontaining organic sulfonates of the cations;

(C) contacting the rst, acid-containing eluent with a weakly basic anionexchange resin to remove the acids in the effluent and produce a iirsteffluent from the anion exchange resin containing substantiallydesalinized water;

(D) regenerating the anion exchange resin by contacting it with asolution containing sodium sulte to remove the acids from the anionexchange resin, restore the material to its basic form, and produce asecond effluent from the anion exchange resin containing inorganicsodium salts of the acid anions, including sodium bisulfate and sodiumbisulfite;

(E) mixing the second effluent from the cation exchange resin with thesecond eluent from the anion exchange resin to form sodium sulte and aprecipitate of calcium sulfate;

(F) filtering off the calcium sulfate;

(G) subsequently heating the combined eluents to remove the aldehyde orketone and sulfur dioxide;

(H) recycling the recovered aldehyde or ketone and sulfur dioxide to atleast partially regenerate the cation exchange material; and

(I) recycling the sodium sulte solution to at least partially regeneratethe anion exchange resin.

6. The process of claim 5, in which the bivalent cations in the waterinclude magnesium, with the magnesium cations forming a precipitate ofmagnesium sulite during the step of heating the combined efuents, and inwhich the magnesium sulte is removed from the sodium sulte solutionbefore it is recycled to the anion exchange resln.

7. The process of claim 6, in which the precipitated magnesium sulite iscalcined to recover sulfur dioxide which is also recycled for reuse inthe regenerant solution for the cation exchange resin.

8. The process of claim 5, in which a water-soluble Cl-Cg aldehyde orketone is used.

9. The process of claim 8, in which ketone is acetone.

10. The process of claim 9, in which the complex sulfonic acid solutioncomprises, by weight, about 12% sulfur dioxide, about 11% acetone, andthe balance water.

11. The process of claim 5, in which the cation exchange material is asulfonic acid resin.

12. The process of claim 5, in which the weak base anion exchange resinis ya water-insoluble crosslinked polymer containing primary, secondary,and tertiary amino groups.

References Cited UNITED STATES PATENTS 2,815,322 12/1957 Higgins 210-333,248,278 4/1966 Wilson 21o-38X SAMIH N. ZAHARNA, Primary Examiner.

